JP7239298B2 - Laser processing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing method for forming pores reaching electrode pads by irradiating the back surface of a substrate with a laser beam.

A wafer in which devices such as ICs and LSIs are partitioned by dividing lines and formed on the surface thereof is divided into individual device chips by a dicing machine and a laser processing machine, and is used in electrical equipment such as mobile phones and personal computers.

In recent years, a hole (via hole) is formed from the back side of the substrate on which the device is formed to the back side of the electrode pad formed on the device, and then a conductive member such as aluminum is embedded in the hole. By stacking the devices on top and bottom, the functionality of the device is enhanced.

In order to form the above pores, the present applicant has proposed a technique of forming pores by irradiating the back surface of the substrate corresponding to the electrode pads of the device with a laser beam (see Patent Document 1). The technique described in Patent Document 1 detects plasma light emitted by irradiating the back surface of a substrate on which a device is formed with a laser beam, and plasma light emitted when the laser beam reaches an electrode pad. , the plasma light is used to determine that the laser beam has reached the electrode pad, thereby stopping the laser beam without making a hole in the electrode pad.

Japanese Patent No. 6034030

According to the above-described prior art, a pulsed laser beam irradiated from the back side of the substrate reaches the electrode pad, and plasma light peculiar to the material constituting the electrode pad is generated. The laser beam can be turned off when the intrinsic plasma light is detected. However, when a pulsed laser beam is repeatedly irradiated at short time intervals (high frequency), it takes time for the plasma light inherent in the substance constituting the substrate to completely disappear even after the laser beam reaches the electrode pad. The plasma light peculiar to the material that constitutes the electrode pad cannot be detected quickly, and as a result, the electrode pad is excessively irradiated with a laser beam, resulting in holes in the electrode pad and proper pore formation. It turns out that it is difficult to

The present invention has been made in view of the above-mentioned facts, and its main technical problem is to provide a laser processing method capable of appropriately forming pores by irradiating a laser beam from the back surface of a substrate corresponding to the electrode pads of a device. to provide.

In order to solve the above main technical problems, according to the present invention, there is provided a laser processing method in which a laser beam is irradiated to the back surface of a substrate on which a device having electrode pads is formed to form pores reaching the electrode pads. a laser beam irradiation step of irradiating a pulsed laser beam from the back surface corresponding to the electrode pad; a detection step of detecting the second plasma light; and a laser irradiation termination step of stopping the irradiation of the laser beam when the second plasma light is detected in the detection step, wherein the laser beam irradiation step comprises: Dispersed irradiation is performed by changing the irradiation position of the laser beam for each pulse, and the time interval of the laser beams irradiated to the same pore is changed to the first laser beam generated by the laser beam previously irradiated to the same pore. A laser processing method is provided in which the time is set to 0.1 ms or longer so that the next laser beam for generating the second plasma light is emitted after the second plasma light is extinguished .

In the laser beam irradiation step, it is preferable to set the time interval to 0.15 ms or longer. Further, in the detection step, the first photodetector detects the first plasma light emitted from the substrate, the second photodetector detects the second plasma light emitted from the electrode pad, and the second photodetector detects the second plasma light emitted from the electrode pad. It is preferable to terminate the irradiation of the laser beam when the output voltage value exceeds a preset threshold voltage value.

The laser processing method of the present invention is a laser processing method in which a laser beam is irradiated to the back surface of a substrate on which a device having an electrode pad is formed to form pores leading to the electrode pads, and the pores correspond to the electrode pads. A laser beam irradiation step of irradiating a pulsed laser beam from the back surface, and the first plasma light emitted from the substrate and the second plasma light emitted from the electrode pad are detected as pores are formed in the substrate by the irradiation of the laser beam. and a laser irradiation termination step of stopping irradiation of the laser beam when the second plasma light is detected in the detection step, and in the laser beam irradiation step, the irradiation position of the laser beam is set to 1 pulse. The time interval between the laser beams irradiated to the same pore is changed after the first plasma beam generated by the laser beam previously irradiated to the same pore is extinguished. , is set to 0.1 ms or longer so that the next laser beam for generating the second plasma light is irradiated . As a result, when the pores reach the electrode pads, the second plasma light can be sufficiently detected, thus solving the problem of holes in the electrode pads.

1 is a perspective view showing a substrate as a workpiece and a mode in which the substrate is supported by a frame in this embodiment; FIG. FIG. 2 is an overall perspective view of a laser processing apparatus for performing laser processing on the substrate shown in FIG. 1; 3 is a block diagram showing an outline of laser beam irradiation means and plasma detection means provided in the laser processing apparatus shown in FIG. 2. FIG. FIG. 4 is a partially enlarged cross-sectional view showing a mode in which pores are formed from the back surface of the substrate in the laser beam irradiation step; 4 is a graph showing changes in outputs (voltage values) of the first photodetector and the second photodetector; FIG. 4 is a waveform diagram showing pulses of a laser beam irradiated in an experiment by the inventors.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a laser processing method based on the present invention will now be described in more detail with reference to the accompanying drawings.

FIG. 1 shows a perspective view of a disk-shaped substrate 10 prepared as a workpiece to be laser-processed in this embodiment. The substrate 10 shown in FIG. 1 is made of, for example, lithium tantalate (LT) with a thickness of 300 μm, and is divided into a plurality of regions by a plurality of division lines 14 arranged in a grid pattern on the surface 10a. A device 12 is formed in each region. A plurality (10) of substantially rectangular electrode pads 12a are formed on the surface of the device 12, as shown in FIG. The electrode pad 12a has a size of about 500 μm×600 μm, and is made of copper (Cu) in the illustrated embodiment. As shown in FIG. 1, the prepared substrate 10 is adhered to and supported by a protective tape T attached to an annular frame F with the front surface 10a facing downward and the back surface 10b facing upward.

FIG. 2 shows an overall perspective view of a laser processing apparatus 1 that carries out laser processing to form pores in a substrate 10 in this embodiment. The laser processing apparatus 1 includes a holding means 20 for holding a substrate 10 supported by a frame F via a protective tape T, a moving means 30 for moving the holding means 20, and a laser beam to the substrate 10 held by the holding means 20. , imaging means 60 for imaging the substrate 10 held by the holding means 20 , and plasma detection means 70 for detecting plasma light emitted from the substrate 10 .

The holding means 20 includes a rectangular X-axis direction movable plate 21 placed on the base 2 so as to be movable in the X-axis direction indicated by an arrow X in the figure, and a rectangular plate 21 perpendicular to the X-axis direction. and a rectangular Y-axis direction movable plate 22 placed on the X-axis direction movable plate 21 so as to be movable in the Y-axis direction indicated by the arrow Y forming a substantially horizontal plane, and fixed to the upper surface of the Y-axis direction movable plate 22 and a rectangular cover plate 26 fixed to the upper end of the post 24 . A circular chuck table 28 extending upward through an elongated hole formed on the cover plate 26 is disposed on the cover plate 26 . A circular suction chuck 40 made of a porous material and extending substantially horizontally is arranged on the upper surface of the chuck table 28 . The suction chuck 40 is connected to suction means (not shown) through a channel passing through the inside of the column 24 . A clamp 42 for fixing a frame F supporting the substrate 10 is arranged on the chuck table 28 .

The moving means 30 is disposed on the base 2 and is provided as a means for relatively moving the holding means 20 and the laser beam irradiation means 50. The X-axis feeds the holding means 20 in the X-axis direction. A moving means 31 and a Y-axis moving means 32 for indexing and feeding the holding means 20 in the Y-axis direction are provided. The X-axis moving means 31 converts the rotational motion of the pulse motor 31a into linear motion via the ball screw 31b and transmits it to the X-axis direction movable plate 21, along the guide rails 2a, 2a on the base 2. The X-axis direction movable plate 21 is advanced and retracted in the X-axis direction. The Y-axis moving means 32 converts the rotary motion of the pulse motor 32a into linear motion via the ball screw 32b, transmits it to the Y-axis direction movable plate 22, and guide rails 21a, 21a on the X-axis direction movable plate 21. , the Y-axis direction movable plate 22 is moved back and forth in the Y-axis direction. Further, a rotation driving means (not shown) is accommodated inside the column 24 so that the position of the chuck table 28 can be rotated to an arbitrary angle and controlled. Although not shown, the X-axis moving means 31, the Y-axis moving means 32, and the rotation driving means (not shown) are provided with position detecting means. The direction position, Y-axis position, and circumferential rotational position are accurately detected and transmitted to the control means 100 (see FIG. 3), which will be described later. Based on this, the X-axis moving means 31, the Y-axis moving means 32, and the rotation driving means (not shown) are driven, and the chuck table 28 can be controlled to achieve a desired X coordinate position, Y coordinate position, and rotation angle θ. It is possible.

A frame 4 is erected on the side of the moving means 30 . The frame 4 includes a vertical wall portion 4a arranged on the base 2 and a horizontal wall portion 4b extending horizontally from the upper end portion of the vertical wall portion 4a. Inside the horizontal wall portion 4b of the frame 4, an optical system of a laser beam irradiation means 50 (not shown) is incorporated. A condensing device 52 constituting a part of the laser beam irradiation means 50 is arranged on the lower surface of the tip portion of the horizontal wall portion 4b.

As shown in FIG. 3, the laser beam irradiation means 50 includes a pulsed laser beam oscillator 51 that oscillates the laser beam LB, an attenuator 53 that adjusts the output of the laser beam LB oscillated by the pulsed laser beam oscillator 51, and an optical path of the laser beam LB that is arbitrarily processed. A first acousto-optic deflection means 54 including at least an acousto-optic element as a light deflection means for controlling deflection in the feed direction (X-axis direction), and a deflection control of the optical path of the laser beam LB in an arbitrary index feed direction (Y-axis direction). a second acousto-optic deflection means 55 including at least an acousto-optic element as a light deflection means; The optical path of the laser beam LB reflected from is guided to a condenser 52 having an fθ lens. The pulsed laser beam oscillator 51, the attenuator 53, the first acousto-optical deflection means 54, and the second acousto-optical deflection means 55 are connected to the control means 100 and operated based on the instruction signal transmitted from the control means 100. is controlled.

When a voltage of, for example, 5 V is applied from the control means 100 to the first acousto-optic deflection means 54 and a frequency corresponding to 5 V is applied to the acousto-optic device (not shown), the pulsed laser beam oscillator 51 oscillates The laser beam LB has its optical axis deflected as indicated by LBa in FIG. When a voltage of, for example, 10 V is applied from the control means 100 to the first acousto-optic deflection means 54 and a frequency corresponding to 10 V is applied to the acousto-optic device, the laser beam oscillated from the pulse laser beam oscillator 51 LB has its optical axis deflected as indicated by LBb in FIG. 3, and is condensed at a condensing point Pb displaced from the condensing point Pa to the right in FIG. 3 by a predetermined amount. Further, when a voltage of, for example, 15 V is applied from the control means 100 to the first acousto-optic deflection means 54 and a frequency corresponding to 15 V is applied to the acousto-optic device, the laser beam oscillated from the pulsed laser beam oscillator 51 LB is deflected as indicated by LBc in FIG. 3, and condensed at a condensing point Pc displaced further to the right in FIG. 3 from the condensing point Pb by a predetermined amount. The second acousto-optic deflection means 55 differs from the above-described first acousto-optic deflection means 54 in that the deflection direction is the indexing direction on the substrate 10 (the Y-axis direction: the direction perpendicular to the drawing). The only difference is that they operate in the same way. In this way, the laser beam LB deflected by the first acousto-optical deflection means 54 and the second acousto-optical deflection means 55 is directed in the machining feed direction (X-axis direction) and the indexing feed direction in accordance with the applied voltage. It can be deflected to any position within a predetermined range (in the Y-axis direction). The laser beam irradiation means 50 shown in FIG. 3 further includes a laser beam LB deflected by the second acousto-optic deflection means 55 when a predetermined voltage is applied to the second acousto-optic deflection means 55. ' (indicated by dashed lines) is provided.

The control means 100 is composed of a computer, and includes a central processing unit (CPU) that executes calculations according to a control program, a read-only memory (ROM) that stores control programs, etc., and stores detected values, calculation results, and the like. It has a read/write random access memory (RAM), an input interface, and an output interface. The control means 100 is connected not only to the laser beam irradiation means 50 described above, but also to the moving means 30, the imaging means 60, the plasma light detection means 70, and the like. is configured to

Returning to FIG. 2 and continuing the description, the imaging means 60 is arranged at a position adjacent to the collector 52 in the X-axis direction on the lower surface of the tip portion of the horizontal wall portion 4b. The imaging means 60 includes a normal imaging element for imaging with visible light, illumination means for illuminating the workpiece, an infrared imaging element, infrared irradiation means, and the like. sent to. The imaging means 60 is used to align the substrate 10 and the light collector 52 when laser processing is performed, and is used to determine the positions of the electrode pads 12a formed on the device 12. used for detection.

The main body portion of the plasma light detection means 70 is housed in the horizontal wall portion 4b of the frame 4, and the plasma light receiving means 71 constituting part of the plasma light detection means 70 is located at the tip of the horizontal wall portion 4b of the frame 4. It is attached at a position adjacent to the light collector 52 in the X-axis direction on the bottom surface, and at a position opposite to the imaging means 60 . The plasma light detection means 70 detects plasma light generated when the substrate 10 held on the chuck table 40 is irradiated with the laser beam LB emitted from the condenser 52 of the laser beam irradiation means 50 as shown in FIG. a plasma light receiving means 71 for receiving light; a beam splitter 72 for splitting the plasma light received by the plasma light receiving means 71 into a first optical path 72a and a second optical path 72b; A first band-pass filter 73 that passes only light of one set wavelength (a wavelength emitted by lithium tantalate forming the substrate of the substrate 10), and light that has passed through the first band-pass filter 73 is received to A first photodetector 74 that outputs an intensity signal, a direction-changing mirror 75 arranged in the second optical path 72b, and a wavelength changed in direction by the direction-changing mirror 75 is the second set wavelength (electrode pad 12 is formed). and a second photodetector 77 for receiving the light passing through the second bandpass filter 76 and outputting a light intensity signal. ing. The plasma light receiving means 71 is composed of a condensing lens (not shown) and a lens case accommodating the condensing lens.

In the illustrated embodiment, the first band-pass filter 73 passes only the wavelength (670 nm) of the first plasma light emitted from lithium tantalate, so that it passes light in the wavelength range of 660 to 680 nm. It is designed to let In addition, in the illustrated embodiment, the second bandpass filter 76 passes only the wavelength (515 nm) of the second plasma light emitted from copper, so that it passes light in the wavelength range of 510 to 520 nm. It's like The first photodetector 74 and the second photodetector 77 output signals of voltage values corresponding to the intensity of the received light to the control means 100 .

The laser processing apparatus 1 used in this embodiment is generally configured as described above. An embodiment of laser processing for forming a pore (via hole) reaching the electrode pad 12a from the back surface 10b side of the substrate 10 will be described.

As described above, the substrate 10 is supported by the annular frame F with the back surface 10b facing upward through the protective tape T. Place the protective tape T side down. Then, the substrate 10 is sucked and held on the chuck table 28 via the protective tape T by activating the suction means (not shown), and the annular frame F is fixed by the clamps 42 .

The chuck table 28 sucking and holding the substrate 10 as described above is positioned directly below the imaging means 60 by the X-axis moving means 31 . When the chuck table 28 is positioned directly below the imaging means 60, check whether the grid-like dividing lines 14 formed on the substrate 10 held by the chuck table 28 are positioned parallel to the X-axis direction and the Y-axis direction. The direction of the substrate 10 is adjusted after confirming whether or not there is. Next, the coordinate positions of the electrode pads 12a formed on each device 12 are detected, and alignment is performed to set the irradiation position of the laser beam LB.

After the alignment is completed, a laser beam irradiation step is performed to irradiate the laser beam LB from the rear surface 10b corresponding to the electrode pad 12a.

(Laser beam irradiation process)
As described above, the laser beam irradiation process is performed after the alignment is completed. The coordinate positions of the devices 12 and the electrode pads 12a on the substrate 10 held by the chuck table 28 are stored and managed by the control means 100, and the electrode pads 12a on the substrate 10 are adjusted by performing the alignment described above. can be positioned accurately at any position.

Here, the laser processing conditions in this embodiment are set as follows, for example.
Laser beam wavelength: 343 nm
Repetition frequency: 50 kHz
Average output: 2W
Pulse energy: 40 μJ
Pulse width: 10ps
Spot diameter: 50 μm

When laser processing is performed under the above-described laser processing conditions, the laser beam LB is radiated specifically in the following manner so that the time interval between the laser beams LB irradiated onto the substrate 10 is 0.1 ms or more. As described above, the repetition frequency of the laser beam LB oscillated from the pulsed laser beam oscillator means 51 is set to 50 kHz. With this setting, the laser beam LB is oscillated at time intervals of 0.02 ms. In this setting, by appropriately controlling the first acousto-optic deflection means 54 and the second acousto-optic deflection means 55, as shown in FIG. Dispersed irradiation is performed by changing the irradiation positions of the laser beams LB1 to LB5 for each pulse corresponding to one electrode pad 12a1 to 12a5. By repeating this, the same pore 16 is irradiated with the laser beam LB oscillated every 0.02 ms at time intervals of 0.1 ms. According to the present embodiment, there is no need to oscillate the useless laser beam LB′ which is discarded to the laser beam absorbing means 57 in order to increase the time interval between the irradiation of the laser beam LB. can be formed, resulting in excellent processing efficiency.

(Detection process)
Along with the laser beam irradiation step described above, a detection step is performed to detect the first plasma light emitted from the lithium tantalate constituting the substrate 10 and the second plasma light emitted from the electrode pad 12a. The detection step will be described below.

In the detection step, while the laser beam irradiation step described above is being performed, light intensity signals are output as voltage values from the first photodetector 74 and the second photodetector 77 of the plasma detection means 70 to the control means 100. be done. FIG. 5 shows the voltage value V(LT) output from the first photodetector 74 that detects the light intensity of the first plasma light and the output from the second photodetector 77 that detects the light intensity of the second plasma light. The voltage value V(Cu) applied is shown over time. In FIG. 5, the horizontal axis indicates time (T), and the vertical axis indicates voltage value (V) corresponding to light intensity.

As shown in FIG. 5, when the irradiation of the electrode pads 12a described above with the laser beam LB is started from the rear surface 10b of the substrate 10, the substrate 10 is irradiated with the laser beam LB, thereby generating the first plasma light. The voltage value V(LT) output from the photodetector 74 begins to rise, reaches a predetermined voltage value (for example, 2.5 V), and remains substantially constant until the laser beam LB reaches the electrode pad 12a. do. After that, when the laser beam LB reaches the electrode pad 12a, the voltage value V(LT) output by the first photodetector 74 begins to drop.

(Laser irradiation end step)
According to the detection process described above, the generation states of the first plasma light and the second plasma light can be detected. By detecting the second plasma light in this detection step, a laser irradiation termination step of stopping the irradiation of the laser beam LB is performed. The laser irradiation ending step will be described more specifically.

When the laser beam LB reaches the electrode pads 12a1-12a5, as shown in FIG. 5, the voltage value V(Cu) output by the second photodetector 77 begins to rise. However, it cannot be said that the pores 16 have sufficiently penetrated the electrode pads 12a1 to 12a5 immediately after the ascent, and there is a possibility that even if the electrically conductive member is buried in the pores 16, defective conduction will occur. In order to cope with this, in the present embodiment , the voltage value V (Cu ) is set to a threshold value S (for example, 1.0 V). The voltage value V(Cu) output from the second photodetector 77 is compared with this threshold value S, and if it is determined that the voltage value V(Cu) exceeds the threshold value S, the pore 16 reaches the electrode pads 12a1 to 12a5 in a sufficient area to form proper pores 16, and the control means 100 issues a stop signal to the laser beam irradiation means 50 to terminate the irradiation of the laser beam LB. It should be noted that if the laser beam irradiation step is continued without performing the above determination based on the threshold value S, the voltage value V (Cu) further increases as indicated by the broken line, and remains at a substantially constant voltage value (e.g., 2.5 V ). However, if the threshold value is raised to this level, there is a risk that through holes will be formed in the electrode pads 12a1 to 12a5, so the threshold value S is set to a value lower than this.

As described above, the laser beam irradiation process, the detection process, and the laser irradiation end process are carried out while processing and feeding the chuck table 28 in the X-axis direction by the X-axis feeding means 31, corresponding to one of the electrode pads 12a1 to 12a5. to form proper pores 16 reaching the electrode pads 12a1 to 12a5. Next, it is determined whether or not the five electrode pads 12a of the devices 12 adjacent in the X-axis direction are positioned in the irradiation area of the laser beam LB immediately below the condenser 52, and the same laser beam irradiation step, detection step, and and a laser irradiation ending step. By repeating this, the pores 16 are formed for all the electrode pads 12a arranged in the X-axis direction. After forming the pores 16 corresponding to all the electrode pads 12a arranged in the X-axis direction, the Y-axis moving means 32 is operated to index and feed the substrate 10 in the Y-axis direction. A series of laser processing similar to that described above is performed on adjacent rows of electrode pads 12a. By repeating these processes, appropriate pores 16 corresponding to all the electrode pads 12a formed on the substrate 10 can be formed.

As described above, in this embodiment, the repetition frequency of the laser beam LB generated by the pulsed laser beam oscillator 51 is set to 50 kHz, that is, the time interval of the pulsed laser beam LB is set to 0.02 ms, The time interval between the laser beams LB applied to the same pores 16 is set to 0.1 ms by irradiating them dispersedly as described above. This is based on the knowledge that, according to the technical idea of the present invention, it is necessary to set the time interval between laser beams irradiated to the same pore 16 to 0.1 ms or more. The grounds for this are explained as follows.

The inventors of the present invention have found that the laser beam LB is irradiated from the back surface 10b of the substrate 10 corresponding to the electrode pad 12a and the time of the laser beam LB irradiated to the same pore 16 for forming the proper pore 16 The following experiment was conducted to examine the interval. The results of the experiment will be described with reference to FIGS. 3 and 6. FIG. FIGS. 6(1) to 6(8) show signal pulses of the laser beam LB irradiated from the rear surface 10b of the substrate 10 by the laser beam irradiation means 50 to correspond to one electrode pad 12a. More specifically, the pulse of the laser beam LB actually applied to the substrate 10 is indicated by a solid line, and the laser beam deflected by the second acousto-optic deflection means 55 so as to deviate from the optical path and is absorbed by the laser beam absorption means 57 and thinned out. LB'
(see FIG. 3) is shown in dashed lines. In addition, the processing conditions other than the parameters whose changes are specified in each of the following experiments are performed in accordance with the processing conditions of the above-described embodiment, and the description of the remaining processing conditions is omitted in the following description.

The standard laser processing conditions in this experiment are as follows.
Wavelength of pulsed laser beam: 343 nm
Repetition frequency: 50 kHz (reference repetition frequency)
Average output: 2W
Pulse energy: 40 μJ
Pulse width: 10ps
Spot diameter: 50 μm

<Experiment 1>
As shown in FIG. 6(1), using the reference repetition frequency (50 kHz: time interval of laser beam LB: 0.02 ms) of the above-described laser processing conditions as it is, a hole 16 is formed at a position corresponding to one electrode pad 12a. was performed, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, holes were formed in the electrode pads 12a.

<Experiment 2>
As shown in FIG. 6(2), among the laser beams LB based on the reference repetition frequency (50 kHz) of the above-described laser processing conditions, the even-numbered laser beams LB are thinned out, that is, they are thinned out one by one, so that the repetition frequency is substantially reduced to 25 kHz (laser beam LB 0.04 ms), laser processing was performed to form the pores 16 at positions corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, holes were formed in the electrode pads 12a.

<Experiment 3>
As shown in FIG. 6(3), out of the laser beams LB based on the reference repetition frequency (50 kHz) of the laser processing conditions described above, the repetition frequency is substantially reduced to approximately 16.7 kHz (the time interval of the laser beam LB is 0) by thinning out two at a time. 06 ms), laser processing was performed to form a pore 16 at a position corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, holes were formed in the electrode pads 12a.

<Experiment 4>
As shown in FIG. 6(4), out of the laser beams LB based on the reference repetition frequency (50 kHz) of the laser processing conditions described above, the repetition frequency is substantially reduced to 12.5 kHz (the time interval of the laser beam LB is 0.5 kHz) by thinning three at a time. 08 ms), laser processing was performed to form a pore 16 at a position corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, the electrode pad 12a was slightly perforated.

<Experiment 5>
As shown in FIG. 6(5), among the laser beams LB based on the reference repetition frequency (50 kHz) of the laser processing conditions described above, the repetition frequency is substantially reduced to 10 kHz (the time interval of the laser beam LB is 0.1 ms) by thinning out four beams at a time. Then, laser processing was performed to form a pore 16 at a position corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, a dent was found on the back surface of the electrode pad 12a, but no hole was made.

<Experiment 6>
As shown in FIG. 6(6), out of the laser beams LB based on the reference repetition frequency (50 kHz) of the laser processing conditions described above, the repetition frequency is substantially reduced to 8.3 kHz (the time interval of the laser beam LB is 0.3 kHz) by thinning out five laser beams at a time. 12 ms), laser processing was performed to form a pore 16 at a position corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, a dent was found on the back surface of the electrode pad 12a, but no hole was made.

<Experiment 7>
As shown in FIG. 6(7), out of the pulsed laser beams LB based on the reference repetition frequency (50 kHz) of the above-described laser processing conditions, the repetition frequency is substantially reduced to 7.1 kHz (the time interval of the laser beams LB is 0 by thinning out 6 pulses at a time). 0.14 ms), laser processing was performed to form a pore 16 at a position corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, a slight dent was found on the back surface of the electrode pad 12a, but no hole was made.

<Experiment 8>
As shown in FIG. 6(8), among the pulsed laser beams LB based on the reference repetition frequency (50 kHz) of the above-described laser processing conditions, the repetition frequency is substantially reduced to 6.25 kHz (the time interval of the laser beams LB is 0 by thinning out seven pulses at a time). 0.16 ms), laser processing was performed to form a pore 16 at a position corresponding to one electrode pad 12a, and the irradiation of the laser beam LB was stopped by detecting the second plasma light. As a result, no holes were formed in the electrode pads 12a, and no dents were observed.

<Conclusion>
From the above experimental results, the present inventors set the substantial repetition frequency of the laser beam LB generated by the pulse laser beam oscillator 51 to 10 kHz or less, that is, set the time interval of the laser beam LB irradiated to the same pore 16 to 0. By setting the time to 1 ms or more, the second plasma light can be sufficiently detected when the pore 16 reaches the electrode pad 12a, and the problem of the electrode pad being perforated can be solved. rice field. Furthermore, by setting the time interval of the laser beam LB to 0.15 ms or more, it is possible to appropriately determine that the pore 16 has reached the electrode pad 12a by detecting the plasma light without causing a large recess in the electrode pad 12a. It has also been found that it is more preferable to set the time interval of the pulsed laser beam LB to 0.15 ms or more in the laser beam irradiation step.

In the above-described embodiment, the repetition frequency of the laser beam LB oscillated by the pulsed laser beam oscillator 51 is set to 50 kHz, and the five electrode pads 12a1 to 12a5 are dispersedly irradiated so that the same pore 16 is irradiated. Although the time interval of the laser beam LB is set to 0.1 ms, the present invention is not limited to this, and the number of electrode pads to be dispersedly irradiated may be adjusted according to the repetition frequency.

Furthermore, as in the experiment described above, the repetition frequency of the laser beam oscillated by the pulsed laser beam oscillator 51 is set to 50 kHz, and the second acoustooptic deflection means 55 is appropriately controlled to remove the unnecessary laser beam LB' from the laser beam. By thinning the laser beams LB by absorbing them in the absorption means 57, the time interval between the laser beams LB irradiated to the same pores 16 can be set to 0.1 ms or more without implementing the dispersion irradiation as described above.

In the above-described embodiment, an example in which the substrate 10 is made of lithium tantalate is shown, but the present invention is not limited to this. The substrate 10 can also be made of other materials such as silicon, lithium niobate (LN), and glass. In that case, since the wavelength of the first plasma light also changes according to the material employed as the substrate 10, the wavelength range to be passed by the beam splitter 72 and the first bandpass filter 73 is adjusted accordingly. . Copper is generally used for the electrode pads 12a, but the present invention does not exclude the use of other materials (for example, gold). In that case, as with the first bandpass filter 73 described above, it is preferable to adjust the wavelengths to be passed by the second bandpass filter 76 in accordance with the metal used.

1: Laser processing device 10: Substrate 12: Device 12a: Electrode pad 121: Inscribed circle 122a: Irradiation area 14: Scheduled dividing line 16: Pore 20: Holding means 21: X-axis direction movable plate 22: Y-axis direction movable Plate 24: Post 26: Cover plate 28: Chuck table 30: Moving means 40: Suction chuck 42: Clamp 50: Laser beam irradiation means 52: Condenser 54: First acousto-optic deflection means 55: Second acousto-optic deflection Means 57: Laser beam absorbing means 60: Imaging means 70: Plasma detecting means 71: Plasma light receiving means 72: Beam splitter 72a: First optical path 72b: Second optical path 73: First bandpass filter 74: First Photodetector 76: Second bandpass filter 77: Second photodetector 100: Control means

Claims (3)

A laser processing method in which a laser beam is irradiated to the back surface of a substrate on which a device having an electrode pad is formed to form a pore reaching the electrode pad,
a laser beam irradiation step of irradiating a pulsed laser beam from the back surface corresponding to the electrode pad;
a detection step of detecting first plasma light emitted from the substrate and second plasma light emitted from the electrode pad while pores are formed in the substrate by irradiating the laser beam;
a laser irradiation termination step of stopping the irradiation of the laser beam when the second plasma light is detected in the detection step;
including at least
In the laser beam irradiation step, dispersion irradiation is performed in which the irradiation position of the laser beam is changed for each pulse, and the time interval of the laser beam irradiated to the same pore is changed to the laser beam that was previously irradiated to the same pore. A laser processing method in which the time is set to 0.1 ms or longer so that the next laser beam for generating the second plasma light is emitted after the first plasma light generated by the above is extinguished. 2. The laser processing method according to claim 1, wherein the time interval is set to 0.15 ms or longer in the laser beam irradiation step. In the detection step, the first photodetector detects the first plasma light emitted from the substrate, the second photodetector detects the second plasma light emitted from the electrode pad, and the second photodetector detects the second plasma light emitted from the electrode pad. 3. The laser processing method according to claim 1, wherein the irradiation of the laser beam is terminated when the voltage value applied exceeds a preset voltage value threshold.

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